Android進(jìn)階事件分發(fā)機(jī)制解決事件沖突
引言
相信伙伴們?cè)谌粘５拈_發(fā)工作中，一定會(huì)遇到事件沖突的問(wèn)題，e.g. 一個(gè)頁(yè)面當(dāng)手指滑動(dòng)的時(shí)候，會(huì)翻到下一頁(yè)；點(diǎn)擊的時(shí)候，需要響應(yīng)頁(yè)面中的元素點(diǎn)擊事件，這個(gè)時(shí)候如果沒(méi)有處理滑動(dòng)事件，可能遇到的問(wèn)題就是在滑動(dòng)翻頁(yè)的時(shí)候卻只響應(yīng)了點(diǎn)擊事件，這個(gè)就是點(diǎn)擊事件與滑動(dòng)事件的沖突。其實(shí)還有很多常見的經(jīng)典事件，e.g. RecyclerView嵌套滑動(dòng)，ViewPager與RecyclerView嵌套滑動(dòng)等，所以這個(gè)時(shí)候我們需要對(duì)事件分發(fā)非常了解，才能針對(duì)需求做相應(yīng)的處理。
1 Android 事件分發(fā)機(jī)制
這是一個(gè)老生常談的問(wèn)題，相信伙伴們都了解常見的Android事件類型：ACTION_DOWN、ACTION_MOVE、ACTION_UP，分別代表手指按下屏幕的事件、手指滑動(dòng)的事件以及手指抬起的事件，那么從手指按下到事件響應(yīng)，中間經(jīng)歷了什么呢？我們從Google的源碼中去尋找答案。
1.1 事件分發(fā)流程
因?yàn)閷?duì)于組件來(lái)說(shuō)，這個(gè)事件要么消費(fèi)要么不消費(fèi)（事件處理），而對(duì)于容器來(lái)說(shuō)，還需要做的一件事就是分發(fā)事件，通常是先分發(fā)后處理，而View就只是處理事件。
因此在進(jìn)行事件沖突處理的時(shí)候，對(duì)于事件是否向下分發(fā)給子View消費(fèi)，就需要在父容器中做攔截，子View僅做事件消費(fèi)。
1.2 View的事件消費(fèi)
首先我們先不看事件是如何分發(fā)的，先關(guān)注下事件是如何被處理的，在View的dispatchTouchEvent方法中，就包含對(duì)事件的處理全過(guò)程。
public boolean dispatchTouchEvent(MotionEvent event) {
//......
boolean result = false;
if (mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onTouchEvent(event, 0);
}
final int actionMasked = event.getActionMasked();
if (actionMasked == MotionEvent.ACTION_DOWN) {
// Defensive cleanup for new gesture
stopNestedScroll();
}
if (onFilterTouchEventForSecurity(event)) {
if ((mViewFlags & ENABLED_MASK) == ENABLED && handleScrollBarDragging(event)) {
result = true;
}
//核心代碼1
ListenerInfo li = mListenerInfo;
if (li != null && li.mOnTouchListener != null
&& (mViewFlags & ENABLED_MASK) == ENABLED
&& li.mOnTouchListener.onTouch(this, event)) {
result = true;
}
//核心代碼2
if (!result && onTouchEvent(event)) {
result = true;
}
}
if (!result && mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onUnhandledEvent(event, 0);
}
// Clean up after nested scrolls if this is the end of a gesture;
// also cancel it if we tried an ACTION_DOWN but we didn't want the rest
// of the gesture.
if (actionMasked == MotionEvent.ACTION_UP ||
actionMasked == MotionEvent.ACTION_CANCEL ||
(actionMasked == MotionEvent.ACTION_DOWN && !result)) {
stopNestedScroll();
}
return result;
}
看到dispatchTouchEvent，我們可能會(huì)想，這個(gè)方法名看著像是分發(fā)事件的方法，View不是僅僅消費(fèi)事件嗎，還需要處理分發(fā)？其實(shí)不是這樣的，因?yàn)閂iew對(duì)于事件可以有選擇的，可以選擇不處理事件，那么就會(huì)往上派給父類去處理這個(gè)事件，如果能夠消費(fèi)，那么就在onTouchEvent中處理了。
核心代碼1：首先拿到一個(gè)ListenerInfo對(duì)象，這個(gè)對(duì)象中標(biāo)記了這個(gè)View設(shè)置的監(jiān)聽事件，這里有幾個(gè)判斷條件：
（1）ListenerInfo不為空，而且設(shè)置了OnTouchListener監(jiān)聽；
（2）設(shè)置了OnTouchListener監(jiān)聽，而且onTouch方法返回了true
這個(gè)時(shí)候，result設(shè)置為true；
核心代碼2：如果滿足了核心代碼1的全部條件，那么核心代碼2就不會(huì)走到onTouchEvent這個(gè)判斷條件中，因?yàn)閞esult = true不滿足條件直接break。
那么如果設(shè)置了OnTouchListener監(jiān)聽，而且onTouch方法返回了false，那么result = false，核心代碼2就能夠執(zhí)行onTouchEvent方法，我們看下這個(gè)方法實(shí)現(xiàn)。
public boolean onTouchEvent(MotionEvent event) {
//......
if (clickable || (viewFlags & TOOLTIP) == TOOLTIP) {
switch (action) {
case MotionEvent.ACTION_UP:
mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN;
if ((viewFlags & TOOLTIP) == TOOLTIP) {
handleTooltipUp();
}
if (!clickable) {
removeTapCallback();
removeLongPressCallback();
mInContextButtonPress = false;
mHasPerformedLongPress = false;
mIgnoreNextUpEvent = false;
break;
}
boolean prepressed = (mPrivateFlags & PFLAG_PREPRESSED) != 0;
if ((mPrivateFlags & PFLAG_PRESSED) != 0 || prepressed) {
// take focus if we don't have it already and we should in
// touch mode.
boolean focusTaken = false;
if (isFocusable() && isFocusableInTouchMode() && !isFocused()) {
focusTaken = requestFocus();
}
if (prepressed) {
// The button is being released before we actually
// showed it as pressed. Make it show the pressed
// state now (before scheduling the click) to ensure
// the user sees it.
setPressed(true, x, y);
}
if (!mHasPerformedLongPress && !mIgnoreNextUpEvent) {
// This is a tap, so remove the longpress check
removeLongPressCallback();
// Only perform take click actions if we were in the pressed state
if (!focusTaken) {
// Use a Runnable and post this rather than calling
// performClick directly. This lets other visual state
// of the view update before click actions start.
if (mPerformClick == null) {
mPerformClick = new PerformClick();
}
if (!post(mPerformClick)) {
performClickInternal();
}
}
}
if (mUnsetPressedState == null) {
mUnsetPressedState = new UnsetPressedState();
}
if (prepressed) {
postDelayed(mUnsetPressedState,
ViewConfiguration.getPressedStateDuration());
} else if (!post(mUnsetPressedState)) {
// If the post failed, unpress right now
mUnsetPressedState.run();
}
removeTapCallback();
}
mIgnoreNextUpEvent = false;
break;
case MotionEvent.ACTION_DOWN:
if (event.getSource() == InputDevice.SOURCE_TOUCHSCREEN) {
mPrivateFlags3 |= PFLAG3_FINGER_DOWN;
}
mHasPerformedLongPress = false;
if (!clickable) {
checkForLongClick(
ViewConfiguration.getLongPressTimeout(),
x,
y,
TOUCH_GESTURE_CLASSIFIED__CLASSIFICATION__LONG_PRESS);
break;
}
if (performButtonActionOnTouchDown(event)) {
break;
}
// Walk up the hierarchy to determine if we're inside a scrolling container.
boolean isInScrollingContainer = isInScrollingContainer();
// For views inside a scrolling container, delay the pressed feedback for
// a short period in case this is a scroll.
if (isInScrollingContainer) {
mPrivateFlags |= PFLAG_PREPRESSED;
if (mPendingCheckForTap == null) {
mPendingCheckForTap = new CheckForTap();
}
mPendingCheckForTap.x = event.getX();
mPendingCheckForTap.y = event.getY();
postDelayed(mPendingCheckForTap, ViewConfiguration.getTapTimeout());
} else {
// Not inside a scrolling container, so show the feedback right away
setPressed(true, x, y);
checkForLongClick(
ViewConfiguration.getLongPressTimeout(),
x,
y,
TOUCH_GESTURE_CLASSIFIED__CLASSIFICATION__LONG_PRESS);
}
break;
//----------注意這里的返回值，clickable為true----------//
return true;
}
//----------注意這里的返回值，clickable為false----------//
return false;
}
這里就是對(duì)所有事件的處理，包括但不限于ACTION_DOWN、ACTION_UP，我們需要知道一點(diǎn)就是，View的click事件其實(shí)是在ACTION_UP中處理的。我們從上面的源碼中可以看出來(lái)，在ACTION_UP中有一個(gè)方法performClickInternal，具體實(shí)現(xiàn)為performClick方法。
public boolean performClick() {
// We still need to call this method to handle the cases where performClick() was called
// externally, instead of through performClickInternal()
notifyAutofillManagerOnClick();
final boolean result;
final ListenerInfo li = mListenerInfo;
if (li != null && li.mOnClickListener != null) {
playSoundEffect(SoundEffectConstants.CLICK);
li.mOnClickListener.onClick(this);
result = true;
} else {
result = false;
}
sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED);
notifyEnterOrExitForAutoFillIfNeeded(true);
return result;
}
在這個(gè)方法中，我們貌似看到同樣的一段代碼，如果設(shè)置了OnClickListener監(jiān)聽，那么就會(huì)執(zhí)行onClick方法也就是響應(yīng)點(diǎn)擊事件。
所以通過(guò)上面的分析，我們能夠了解，如果同一個(gè)View同時(shí)設(shè)置了setOnClickListener和setOnTouchListener，如果setOnTouchListener返回了false，那么點(diǎn)擊事件是可以響應(yīng)的；如果setOnTouchListener返回了true，那么點(diǎn)擊事件將不再響應(yīng)。
binding.tvHello.setOnClickListener {
Log.e("TAG","OnClick")
}
binding.tvHello.setOnTouchListener(object : View.OnTouchListener{
override fun onTouch(v: View?, event: MotionEvent?): Boolean {
Log.e("TAG","onTouch")
return false
}
})
還需要注意一點(diǎn)的就是，對(duì)于clickable這個(gè)屬性要求非常嚴(yán)格，必須要設(shè)置為true才可以進(jìn)行事件的消費(fèi)，也就是說(shuō)在clickable為true的時(shí)候，onTouchEvent才會(huì)返回true，否則就會(huì)返回false，這個(gè)DOWN事件沒(méi)有被消費(fèi)，也就是說(shuō)在dispatchTransformedTouchEvent方法中返回了false，此時(shí)就不會(huì)給 mFirstTouchTraget == null 賦值，后續(xù)MOVE事件進(jìn)來(lái)就不會(huì)處理，這里需要非常注意。
這里伙伴們?nèi)绻焕斫?，可以換句話說(shuō)：就是當(dāng)DOWN事件來(lái)臨之后，其實(shí)ViewGroup一定會(huì)將事件分發(fā)給子View，看子View要不要消費(fèi)，如果子View不是clickable的，也就是說(shuō)clickable = false，那么此時(shí)子View的onTouchEvent返回false，那么dispatchTouchEvent也是返回false，代表子View不消費(fèi)這個(gè)事件，那么此時(shí)dispatchTransformedTouchEvent也是返回了false，mFirstTouchTraget還是空；因?yàn)?strong>子View沒(méi)有消費(fèi)DOWN事件，那么后續(xù)事件不會(huì)再觸發(fā)了。
1.3 ViewGroup的事件分發(fā) -- ACTION_DOWN
前面我們介紹了View對(duì)于事件的消費(fèi)，不管是click還是touch，都有對(duì)應(yīng)的標(biāo)準(zhǔn)決定是否能夠響應(yīng)事件，最終View的dispatchTouchEvent返回值，就是result的值，只要有一個(gè)事件被消費(fèi)，那么這個(gè)事件就算是到頭了，但是，如果最終事件沒(méi)有被消費(fèi)，也就是說(shuō)dispatchTouchEvent返回了false，那么父容器就能夠拿到這個(gè)狀態(tài)，決定誰(shuí)去處理這個(gè)事件。
所以ViewGroup就像是荷官，卡牌就是事件，她可以決定牌發(fā)到誰(shuí)的手里，所以ViewGroup的事件分發(fā)機(jī)制核心就在于dispatchTouchEvent方法。
public boolean dispatchTouchEvent(MotionEvent ev) {
// ......
if (onFilterTouchEventForSecurity(ev)) {
final int action = ev.getAction();
final int actionMasked = action & MotionEvent.ACTION_MASK;
// Handle an initial down.
if (actionMasked == MotionEvent.ACTION_DOWN) {
// Throw away all previous state when starting a new touch gesture.
// The framework may have dropped the up or cancel event for the previous gesture
// due to an app switch, ANR, or some other state change.
cancelAndClearTouchTargets(ev);
resetTouchState();
}
// Check for interception.
final boolean intercepted;
if (actionMasked == MotionEvent.ACTION_DOWN
|| mFirstTouchTarget != null) {
final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
if (!disallowIntercept) {
intercepted = onInterceptTouchEvent(ev);
ev.setAction(action); // restore action in case it was changed
} else {
intercepted = false;
}
} else {
// There are no touch targets and this action is not an initial down
// so this view group continues to intercept touches.
intercepted = true;
}
// If intercepted, start normal event dispatch. Also if there is already
// a view that is handling the gesture, do normal event dispatch.
if (intercepted || mFirstTouchTarget != null) {
ev.setTargetAccessibilityFocus(false);
}
// Check for cancelation.
final boolean canceled = resetCancelNextUpFlag(this)
|| actionMasked == MotionEvent.ACTION_CANCEL;
// Update list of touch targets for pointer down, if needed.
final boolean isMouseEvent = ev.getSource() == InputDevice.SOURCE_MOUSE;
final boolean split = (mGroupFlags & FLAG_SPLIT_MOTION_EVENTS) != 0
&& !isMouseEvent;
TouchTarget newTouchTarget = null;
boolean alreadyDispatchedToNewTouchTarget = false;
// -------- 這里是不攔截的時(shí)候會(huì)走的地方 -------//
if (!canceled && !intercepted) {
// If the event is targeting accessibility focus we give it to the
// view that has accessibility focus and if it does not handle it
// we clear the flag and dispatch the event to all children as usual.
// We are looking up the accessibility focused host to avoid keeping
// state since these events are very rare.
View childWithAccessibilityFocus = ev.isTargetAccessibilityFocus()
? findChildWithAccessibilityFocus() : null;
if (actionMasked == MotionEvent.ACTION_DOWN
|| (split && actionMasked == MotionEvent.ACTION_POINTER_DOWN)
|| actionMasked == MotionEvent.ACTION_HOVER_MOVE) {
final int actionIndex = ev.getActionIndex(); // always 0 for down
final int idBitsToAssign = split ? 1 << ev.getPointerId(actionIndex)
: TouchTarget.ALL_POINTER_IDS;
// Clean up earlier touch targets for this pointer id in case they
// have become out of sync.
removePointersFromTouchTargets(idBitsToAssign);
final int childrenCount = mChildrenCount;
if (newTouchTarget == null && childrenCount != 0) {
final float x =
isMouseEvent ? ev.getXCursorPosition() : ev.getX(actionIndex);
final float y =
isMouseEvent ? ev.getYCursorPosition() : ev.getY(actionIndex);
// Find a child that can receive the event.
// Scan children from front to back.
final ArrayList<View> preorderedList = buildTouchDispatchChildList();
final boolean customOrder = preorderedList == null
&& isChildrenDrawingOrderEnabled();
final View[] children = mChildren;
for (int i = childrenCount - 1; i >= 0; i--) {
final int childIndex = getAndVerifyPreorderedIndex(
childrenCount, i, customOrder);
final View child = getAndVerifyPreorderedView(
preorderedList, children, childIndex);
// If there is a view that has accessibility focus we want it
// to get the event first and if not handled we will perform a
// normal dispatch. We may do a double iteration but this is
// safer given the timeframe.
if (childWithAccessibilityFocus != null) {
if (childWithAccessibilityFocus != child) {
continue;
}
childWithAccessibilityFocus = null;
i = childrenCount - 1;
}
if (!child.canReceivePointerEvents()
|| !isTransformedTouchPointInView(x, y, child, null)) {
ev.setTargetAccessibilityFocus(false);
continue;
}
newTouchTarget = getTouchTarget(child);
if (newTouchTarget != null) {
// Child is already receiving touch within its bounds.
// Give it the new pointer in addition to the ones it is handling.
newTouchTarget.pointerIdBits |= idBitsToAssign;
break;
}
resetCancelNextUpFlag(child);
if (dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)) {
// Child wants to receive touch within its bounds.
mLastTouchDownTime = ev.getDownTime();
if (preorderedList != null) {
// childIndex points into presorted list, find original index
for (int j = 0; j < childrenCount; j++) {
if (children[childIndex] == mChildren[j]) {
mLastTouchDownIndex = j;
break;
}
}
} else {
mLastTouchDownIndex = childIndex;
}
mLastTouchDownX = ev.getX();
mLastTouchDownY = ev.getY();
newTouchTarget = addTouchTarget(child, idBitsToAssign);
alreadyDispatchedToNewTouchTarget = true;
break;
}
// The accessibility focus didn't handle the event, so clear
// the flag and do a normal dispatch to all children.
ev.setTargetAccessibilityFocus(false);
}
if (preorderedList != null) preorderedList.clear();
}
if (newTouchTarget == null && mFirstTouchTarget != null) {
// Did not find a child to receive the event.
// Assign the pointer to the least recently added target.
newTouchTarget = mFirstTouchTarget;
while (newTouchTarget.next != null) {
newTouchTarget = newTouchTarget.next;
}
newTouchTarget.pointerIdBits |= idBitsToAssign;
}
}
}
//-------------這里是攔截之后會(huì)走的地方-------------//
// Dispatch to touch targets.
if (mFirstTouchTarget == null) {
// No touch targets so treat this as an ordinary view.
handled = dispatchTransformedTouchEvent(ev, canceled, null,
TouchTarget.ALL_POINTER_IDS);
} else {
// Dispatch to touch targets, excluding the new touch target if we already
// dispatched to it. Cancel touch targets if necessary.
TouchTarget predecessor = null;
TouchTarget target = mFirstTouchTarget;
while (target != null) {
final TouchTarget next = target.next;
if (alreadyDispatchedToNewTouchTarget && target == newTouchTarget) {
handled = true;
} else {
final boolean cancelChild = resetCancelNextUpFlag(target.child)
|| intercepted;
if (dispatchTransformedTouchEvent(ev, cancelChild,
target.child, target.pointerIdBits)) {
handled = true;
}
if (cancelChild) {
if (predecessor == null) {
mFirstTouchTarget = next;
} else {
predecessor.next = next;
}
target.recycle();
target = next;
continue;
}
}
predecessor = target;
target = next;
}
}
// Update list of touch targets for pointer up or cancel, if needed.
if (canceled
|| actionMasked == MotionEvent.ACTION_UP
|| actionMasked == MotionEvent.ACTION_HOVER_MOVE) {
resetTouchState();
} else if (split && actionMasked == MotionEvent.ACTION_POINTER_UP) {
final int actionIndex = ev.getActionIndex();
final int idBitsToRemove = 1 << ev.getPointerId(actionIndex);
removePointersFromTouchTargets(idBitsToRemove);
}
}
if (!handled && mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onUnhandledEvent(ev, 1);
}
return handled;
}
1.1.1 萬(wàn)事皆始于ACTION_DOWN
看著dispatchTouchEvent這么長(zhǎng)的代碼，是不是腦袋都昏了，我給伙伴們分下層，首先一切的事件分發(fā)都是從ACTION_DOWN事件開始，所以我們可以看下ACTION_DOWN事件是如何處理的。
核心代碼1：
final boolean intercepted;
if (actionMasked == MotionEvent.ACTION_DOWN
|| mFirstTouchTarget != null) {
final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
if (!disallowIntercept) {
intercepted = onInterceptTouchEvent(ev);
ev.setAction(action); // restore action in case it was changed
} else {
intercepted = false;
}
} else {
// There are no touch targets and this action is not an initial down
// so this view group continues to intercept touches.
intercepted = true;
}
當(dāng)ACTION_DWON事件來(lái)了之后，首先調(diào)用ViewGroup的dispatchTouchEvent方法，在上面這段代碼中，就是判斷ViewGroup是否要攔截這個(gè)事件，如果DOWN事件都被攔截了，就沒(méi)有小弟的份了。
所以如果當(dāng)前是DOWN事件，或者mFirstTouchTarget不為空。首先這里有一個(gè)變量mFirstTouchTarget，我們可以認(rèn)為這個(gè)就是可能會(huì)消費(fèi)事件的View，因?yàn)槭状慰隙榭眨钱?dāng)前為DOWN事件，所以這個(gè)條件是滿足的，那么就會(huì)進(jìn)入到代碼塊中。
在代碼塊中，有一個(gè)disallowIntercept變量，這個(gè)變量標(biāo)志著子View是否需要消費(fèi)這個(gè)事件，如果需要消費(fèi)這個(gè)事件，子View可以調(diào)用requestDisallowInterceptTouchEvent這個(gè)方法，設(shè)置為true，那么父容器就不會(huì)攔截。
所以如果子View需要消費(fèi)這個(gè)事件，那么disallowIntercept = true，這個(gè)時(shí)候intercepted = false，意味著父容器不會(huì)攔截；如果子View不消費(fèi)這個(gè)事件，那么disallowIntercept = false，然后會(huì)判斷ViewGroup中的onInterceptTouchEvent方法，是否由父容器消費(fèi)這個(gè)事件從而決定intercepted的值。
所以看到這里，其實(shí)我們?cè)诮鉀Q事件沖突的時(shí)候就會(huì)有兩種方式：一種就是重寫父容器的onInterceptTouchEvent方法，由父容器決定是否攔截；另一種就是由子View調(diào)用requestDisallowInterceptTouchEvent方法，通知父容器是否能夠攔截。
那么假設(shè)，當(dāng)前ViewGroup要攔截這個(gè)事件，也就是在onInterceptTouchEvent中返回了true
override fun onInterceptTouchEvent(ev: MotionEvent?): Boolean {
return true
}
1.1.2 ViewGroup攔截事件
那么既然攔截了事件，那么當(dāng)前ViewGroup就需要決定到底處不處理事件，如果不處理就需要向上傳遞。
因?yàn)閂iewGroup攔截了事件，因此intercepted = true，在1.3開頭的代碼中，我標(biāo)記了2個(gè)位置，一個(gè)是攔截會(huì)走的位置，一個(gè)是沒(méi)有攔截會(huì)走的位置。
核心代碼2：
if (mFirstTouchTarget == null) {
// No touch targets so treat this as an ordinary view.
handled = dispatchTransformedTouchEvent(ev, canceled, null,
TouchTarget.ALL_POINTER_IDS);
} else {
// Dispatch to touch targets, excluding the new touch target if we already
// dispatched to it. Cancel touch targets if necessary.
TouchTarget predecessor = null;
TouchTarget target = mFirstTouchTarget;
while (target != null) {
final TouchTarget next = target.next;
if (alreadyDispatchedToNewTouchTarget && target == newTouchTarget) {
handled = true;
} else {
final boolean cancelChild = resetCancelNextUpFlag(target.child)
|| intercepted;
if (dispatchTransformedTouchEvent(ev, cancelChild,
target.child, target.pointerIdBits)) {
handled = true;
}
if (cancelChild) {
if (predecessor == null) {
mFirstTouchTarget = next;
} else {
predecessor.next = next;
}
target.recycle();
target = next;
continue;
}
}
predecessor = target;
target = next;
}
}
因?yàn)檫@個(gè)時(shí)候，mFirstTouchTarget還是為空的，所以會(huì)調(diào)用dispatchTransformedTouchEvent方法。
private boolean dispatchTransformedTouchEvent(MotionEvent event, boolean cancel,
View child, int desiredPointerIdBits) {
final boolean handled;
// ......
// Perform any necessary transformations and dispatch.
if (child == null) {
handled = super.dispatchTouchEvent(transformedEvent);
} else {
final float offsetX = mScrollX - child.mLeft;
final float offsetY = mScrollY - child.mTop;
transformedEvent.offsetLocation(offsetX, offsetY);
if (! child.hasIdentityMatrix()) {
transformedEvent.transform(child.getInverseMatrix());
}
handled = child.dispatchTouchEvent(transformedEvent);
}
// Done.
transformedEvent.recycle();
return handled;
}
這時(shí)候需要注意一點(diǎn)，這個(gè)方法第三個(gè)參數(shù)為null； 所以當(dāng)child為空的時(shí)候，就會(huì)調(diào)用父類的dispatchTouchEvent，也就是View的dispatchTouchEvent方法，在1.2小節(jié)中我們是對(duì)這個(gè)方法做過(guò)分析的，也是會(huì)決定是否處理這個(gè)事件，最終返回是否處理的結(jié)果。
所以這一次的結(jié)果（handled的值）最終決定了當(dāng)前ViewGroup是否會(huì)處理這個(gè)事件，如果不處理，那么就扔到上級(jí)再判斷。
1.1.3 ViewGroup不攔截事件
如果ViewGroup不攔截事件，那么intercepted = false，所以會(huì)走到分發(fā)事件的代碼中。
核心代碼3：
if (!canceled && !intercepted) {
if (actionMasked == MotionEvent.ACTION_DOWN
|| (split && actionMasked == MotionEvent.ACTION_POINTER_DOWN)
|| actionMasked == MotionEvent.ACTION_HOVER_MOVE) {
final int actionIndex = ev.getActionIndex(); // always 0 for down
final int idBitsToAssign = split ? 1 << ev.getPointerId(actionIndex)
: TouchTarget.ALL_POINTER_IDS;
// Clean up earlier touch targets for this pointer id in case they
// have become out of sync.
removePointersFromTouchTargets(idBitsToAssign);
final int childrenCount = mChildrenCount;
if (newTouchTarget == null && childrenCount != 0) {
final float x =
isMouseEvent ? ev.getXCursorPosition() : ev.getX(actionIndex);
final float y =
isMouseEvent ? ev.getYCursorPosition() : ev.getY(actionIndex);
// Find a child that can receive the event.
// Scan children from front to back.
final ArrayList<View> preorderedList = buildTouchDispatchChildList();
final boolean customOrder = preorderedList == null
&& isChildrenDrawingOrderEnabled();
final View[] children = mChildren;
//----------遍歷集合，從后往前取------------//
for (int i = childrenCount - 1; i >= 0; i--) {
final int childIndex = getAndVerifyPreorderedIndex(
childrenCount, i, customOrder);
final View child = getAndVerifyPreorderedView(
preorderedList, children, childIndex);
// If there is a view that has accessibility focus we want it
// to get the event first and if not handled we will perform a
// normal dispatch. We may do a double iteration but this is
// safer given the timeframe.
if (childWithAccessibilityFocus != null) {
if (childWithAccessibilityFocus != child) {
continue;
}
childWithAccessibilityFocus = null;
i = childrenCount - 1;
}
//-----判斷View是否有消費(fèi)的可能性---------//
if (!child.canReceivePointerEvents()
|| !isTransformedTouchPointInView(x, y, child, null)) {
ev.setTargetAccessibilityFocus(false);
continue;
}
newTouchTarget = getTouchTarget(child);
if (newTouchTarget != null) {
// Child is already receiving touch within its bounds.
// Give it the new pointer in addition to the ones it is handling.
newTouchTarget.pointerIdBits |= idBitsToAssign;
break;
}
resetCancelNextUpFlag(child);
//-------- 這個(gè)方法需要注意，第三個(gè)參數(shù)不為空----------//
if (dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)) {
// Child wants to receive touch within its bounds.
mLastTouchDownTime = ev.getDownTime();
if (preorderedList != null) {
// childIndex points into presorted list, find original index
for (int j = 0; j < childrenCount; j++) {
if (children[childIndex] == mChildren[j]) {
mLastTouchDownIndex = j;
break;
}
}
} else {
mLastTouchDownIndex = childIndex;
}
mLastTouchDownX = ev.getX();
mLastTouchDownY = ev.getY();
newTouchTarget = addTouchTarget(child, idBitsToAssign);
alreadyDispatchedToNewTouchTarget = true;
break;
}
// The accessibility focus didn't handle the event, so clear
// the flag and do a normal dispatch to all children.
ev.setTargetAccessibilityFocus(false);
}
if (preorderedList != null) preorderedList.clear();
}
if (newTouchTarget == null && mFirstTouchTarget != null) {
// Did not find a child to receive the event.
// Assign the pointer to the least recently added target.
newTouchTarget = mFirstTouchTarget;
while (newTouchTarget.next != null) {
newTouchTarget = newTouchTarget.next;
}
newTouchTarget.pointerIdBits |= idBitsToAssign;
}
}
}
這里首先會(huì)判斷事件是否為down事件，只有down事件才會(huì)分發(fā)，如果是move或者up事件便不會(huì)分發(fā)。所以伙伴們需要牢記一點(diǎn)，如果在某個(gè)控件上產(chǎn)生了up事件，即便是設(shè)置了onClickListener，因?yàn)闆](méi)有接收到down事件，所以也不會(huì)響應(yīng)點(diǎn)擊事件。
然后調(diào)用buildTouchDispatchChildList方法，對(duì)當(dāng)前ViewGroup全部的子View根據(jù)Z軸順序排序，
ArrayList<View> buildOrderedChildList() {
final int childrenCount = mChildrenCount;
if (childrenCount <= 1 || !hasChildWithZ()) return null;
if (mPreSortedChildren == null) {
mPreSortedChildren = new ArrayList<>(childrenCount);
} else {
// callers should clear, so clear shouldn't be necessary, but for safety...
mPreSortedChildren.clear();
mPreSortedChildren.ensureCapacity(childrenCount);
}
final boolean customOrder = isChildrenDrawingOrderEnabled();
for (int i = 0; i < childrenCount; i++) {
// add next child (in child order) to end of list
final int childIndex = getAndVerifyPreorderedIndex(childrenCount, i, customOrder);
final View nextChild = mChildren[childIndex];
final float currentZ = nextChild.getZ();
// insert ahead of any Views with greater Z
int insertIndex = i;
while (insertIndex > 0 && mPreSortedChildren.get(insertIndex - 1).getZ() > currentZ) {
insertIndex--;
}
mPreSortedChildren.add(insertIndex, nextChild);
}
return mPreSortedChildren;
}
這里我們可以看到是按照Z(yǔ)軸值從高到低排序，Z值越大，說(shuō)明其層級(jí)越深，最終拿到一個(gè)View的集合。
然后遍歷取值的時(shí)候，是按照倒序取值的方式，因?yàn)閆值越小，說(shuō)明其層級(jí)越淺，事件被消費(fèi)的概率就越高；取出一個(gè)View之后，首先需要判斷它是否具備消費(fèi)事件的可能性。
if (!child.canReceivePointerEvents()
|| !isTransformedTouchPointInView(x, y, child, null)) {
ev.setTargetAccessibilityFocus(false);
continue;
}
第一個(gè)條件：View是可見的，或者 getAnimation() != null
protected boolean canReceivePointerEvents() {
return (mViewFlags & VISIBILITY_MASK) == VISIBLE || getAnimation() != null;
}
第二個(gè)條件：當(dāng)前View在點(diǎn)擊（x,y）的范圍之內(nèi)，如果離著手指點(diǎn)擊的位置很遠(yuǎn)，肯定不可能消費(fèi)。
protected boolean isTransformedTouchPointInView(float x, float y, View child,
PointF outLocalPoint) {
final float[] point = getTempLocationF();
point[0] = x;
point[1] = y;
transformPointToViewLocal(point, child);
final boolean isInView = child.pointInView(point[0], point[1]);
if (isInView && outLocalPoint != null) {
outLocalPoint.set(point[0], point[1]);
}
return isInView;
}
所以經(jīng)過(guò)層層篩選，也就只剩下一小部分可能會(huì)消費(fèi)事件的View，那么怎么把他揪出來(lái)呢？經(jīng)過(guò)篩選的View最終調(diào)用了dispatchTransformedTouchEvent方法，在1.1.2中我們介紹了這個(gè)方法，就是用來(lái)判斷是否消費(fèi)事件的，這里傳入的第三個(gè)參數(shù)不為空！
回到前面dispatchTransformedTouchEvent方法中，當(dāng)child不為空的時(shí)候，走到else代碼塊中，最終還是調(diào)用了child的dispatchTouchEvent方法。
所以如果當(dāng)前View消費(fèi)了DOWN事件，那么返回值為true，也就是dispatchTransformedTouchEvent返回了true，那么會(huì)進(jìn)入下面代碼塊中。
if (dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)) {
// Child wants to receive touch within its bounds.
mLastTouchDownTime = ev.getDownTime();
if (preorderedList != null) {
// childIndex points into presorted list, find original index
for (int j = 0; j < childrenCount; j++) {
if (children[childIndex] == mChildren[j]) {
mLastTouchDownIndex = j;
break;
}
}
} else {
mLastTouchDownIndex = childIndex;
}
mLastTouchDownX = ev.getX();
mLastTouchDownY = ev.getY();
//----- 這里就是給mFirstTouchTarget賦值--------//
newTouchTarget = addTouchTarget(child, idBitsToAssign);
alreadyDispatchedToNewTouchTarget = true;
break;
}
因?yàn)楫?dāng)前child消費(fèi)了事件，那么我們前面提到的mFirstTouchTarget就是由child封裝一層得來(lái)的，也就是調(diào)用了addTouchTarget方法，也就是說(shuō)當(dāng)一個(gè)child消費(fèi)了一個(gè)DOWN事件之后，mFirstTouchTarget就不再為空了。
private TouchTarget addTouchTarget(@NonNull View child, int pointerIdBits) {
final TouchTarget target = TouchTarget.obtain(child, pointerIdBits);
target.next = mFirstTouchTarget;
mFirstTouchTarget = target;
return target;
}
如果全部都不處理，那么mFirstTouchTarget還是為空，走到下面還是會(huì)執(zhí)行ViewGroup攔截事件的邏輯，也就是1.1.2中的邏輯，所以說(shuō)，如果全部的子View都不處理，其實(shí)跟ViewGroup攔截事件的本質(zhì)是一致的。
1.4 ViewGroup的事件分發(fā) -- ACTION_MOVE
前面我們介紹了ViewGroup對(duì)于ACTION_DOWN事件的分發(fā)處理，因?yàn)镈OWN事件只有一次，MOVE可以有無(wú)數(shù)次，所以在處理完DOWN事件之后，就會(huì)有MOVE事件涌進(jìn)來(lái)。
所以還是回到前面的判斷條件中，我們對(duì)于MOVE事件的分發(fā)，需要基于DOWN事件的處理；
final boolean intercepted;
if (actionMasked == MotionEvent.ACTION_DOWN
|| mFirstTouchTarget != null) {
final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
if (!disallowIntercept) {
intercepted = onInterceptTouchEvent(ev);
ev.setAction(action); // restore action in case it was changed
} else {
intercepted = false;
}
} else {
// There are no touch targets and this action is not an initial down
// so this view group continues to intercept touches.
intercepted = true;
}
如果ViewGroup攔截了事件：
那么mFirstTouchTarget == null，會(huì)走到else中，此時(shí) intercepted = true，那么就會(huì)走到ViewGroup攔截邏輯中，會(huì)調(diào)用dispatchTransformedTouchEvent，第三個(gè)參數(shù)child == null，那么如果ViewGroup不消費(fèi)不處理，就會(huì)交給上級(jí)處理。
如果ViewGroup不攔截事件：
那么mFirstTouchTarget != null，此時(shí)還是會(huì)判斷子View是否攔截該事件，如果攔截，那么intercepted = true，還是會(huì)走上面的攔截邏輯；如果不攔截，那么intercepted = false，會(huì)走到ViewGroup不攔截事件的邏輯中。
if (newTouchTarget == null && mFirstTouchTarget != null) {
// Did not find a child to receive the event.
// Assign the pointer to the least recently added target.
newTouchTarget = mFirstTouchTarget;
while (newTouchTarget.next != null) {
newTouchTarget = newTouchTarget.next;
}
newTouchTarget.pointerIdBits |= idBitsToAssign;
}
因?yàn)?strong>只有DOWN事件的時(shí)候，才會(huì)遍歷View樹，如果是MOVE事件，不會(huì)進(jìn)入循環(huán)，不再分發(fā)，而是走上面的邏輯，此時(shí)newTouchTarget == null 而且 mFirstTouchTarget不為空，此時(shí)會(huì)給newTouchTarget重新賦值，然后繼續(xù)往下走。
if (mFirstTouchTarget == null) {
// No touch targets so treat this as an ordinary view.
handled = dispatchTransformedTouchEvent(ev, canceled, null,
TouchTarget.ALL_POINTER_IDS);
} else {
// Dispatch to touch targets, excluding the new touch target if we already
// dispatched to it. Cancel touch targets if necessary.
TouchTarget predecessor = null;
TouchTarget target = mFirstTouchTarget;
while (target != null) {
final TouchTarget next = target.next;
if (alreadyDispatchedToNewTouchTarget && target == newTouchTarget) {
handled = true;
} else {
final boolean cancelChild = resetCancelNextUpFlag(target.child)
|| intercepted;
if (dispatchTransformedTouchEvent(ev, cancelChild,
target.child, target.pointerIdBits)) {
handled = true;
}
if (cancelChild) {
if (predecessor == null) {
mFirstTouchTarget = next;
} else {
predecessor.next = next;
}
target.recycle();
target = next;
continue;
}
}
predecessor = target;
target = next;
}
}
因?yàn)閙FirstTouchTarget != null，因此會(huì)走到else代碼塊中，因?yàn)閍lreadyDispatchedToNewTouchTarget是在事件分發(fā)時(shí)才賦值為true，所以在while循環(huán)中（一次循環(huán)，單點(diǎn)觸控），會(huì)走else代碼塊，其實(shí)還是會(huì)調(diào)用dispatchTransformedTouchEvent方法判斷是否處理事件，所以這就形成了一條責(zé)任鏈，當(dāng)一個(gè)View消費(fèi)了DOWN事件之后，后續(xù)的事件系統(tǒng)默認(rèn)都會(huì)給他消費(fèi)，除非特殊情況。
2 Android事件沖突處理
基于Android事件分發(fā)機(jī)制，DOWN事件只會(huì)執(zhí)行一次，而且只是做分發(fā)工作，而MOVE事件會(huì)有無(wú)數(shù)次，所以對(duì)于事件沖突來(lái)說(shuō)，只能在MOVE事件中進(jìn)行處理。
if (actionMasked == MotionEvent.ACTION_DOWN
|| mFirstTouchTarget != null) {
final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
if (!disallowIntercept) {
intercepted = onInterceptTouchEvent(ev);
ev.setAction(action); // restore action in case it was changed
} else {
intercepted = false;
}
} else {
// There are no touch targets and this action is not an initial down
// so this view group continues to intercept touches.
intercepted = true;
}
針對(duì)這種分發(fā)機(jī)制，前面也提到了兩種處理方式，要么在父容器的onInterceptTouchEvent中判斷是否攔截事件，要么控制disallowIntercept的值，所以就出現(xiàn)了2種攔截法。
2.1 內(nèi)部攔截法
此方式指的是在子View中，通過(guò)控制disallowIntercept的值，來(lái)讓父容器決定是否攔截事件。
class MotionEventLayout(
val mContext: Context,
val attrs: AttributeSet? = null,
val defStyleAttr: Int = 0
) : FrameLayout(mContext, attrs, defStyleAttr) {
override fun onInterceptTouchEvent(ev: MotionEvent?): Boolean {
return true
}
}
如果在父容器的onInterceptTouchEvent方法中返回true，那么down一定會(huì)被攔截而不會(huì)分發(fā)給子View，所以子View不會(huì)響應(yīng)任何事件。
class MotionEventChildLayout(
val mContext: Context,
val attrs: AttributeSet? = null,
val defStyleAttr: Int = 0
) : FrameLayout(mContext, attrs, defStyleAttr) {
private var startX = 0
private var startY = 0
override fun dispatchTouchEvent(ev: MotionEvent?): Boolean {
when (ev?.action) {
MotionEvent.ACTION_DOWN -> {
//不能被攔截
parent.requestDisallowInterceptTouchEvent(true)
}
MotionEvent.ACTION_MOVE -> {
var endX = ev.rawX
var endY = ev.rawY
//豎向滑動(dòng)
if (abs(endX - startX) > abs(endY - startY)) {
parent.requestDisallowInterceptTouchEvent(false)
}
startX = endX
startY = endY
}
}
return super.dispatchTouchEvent(ev)
}
}
所以使用內(nèi)部攔截法時(shí)，對(duì)于DOWN事件不能被攔截，需要將requestDisallowInterceptTouchEvent設(shè)置為true，這樣父容器在分發(fā)事件時(shí)，就不會(huì)走自身的onInterceptTouchEvent方法（此時(shí)無(wú)論設(shè)置true或者false都是無(wú)效的），intercepted = false，此時(shí)事件就會(huì)被分發(fā)到子View。
然后在滑動(dòng)時(shí)，如果父容器支持左右滑動(dòng)，子View支持上下滑動(dòng)，那么就可以判斷：如果橫向滑動(dòng)的距離大于豎直方向滑動(dòng)的距離，任務(wù)在左右滑動(dòng)，此時(shí)事件處理交給父容器處理；反之則交給子View處理。
這是我們理解中的處理方式，看著好像沒(méi)問(wèn)題，但是實(shí)際運(yùn)行時(shí)發(fā)現(xiàn)無(wú)效??！ 我們明明設(shè)置了requestDisallowInterceptTouchEvent為true，為什么沒(méi)生效呢？
if (actionMasked == MotionEvent.ACTION_DOWN) {
// Throw away all previous state when starting a new touch gesture.
// The framework may have dropped the up or cancel event for the previous gesture
// due to an app switch, ANR, or some other state change.
cancelAndClearTouchTargets(ev);
resetTouchState();
}
通過(guò)源碼我們發(fā)現(xiàn)，當(dāng)DOWN事件觸發(fā)之后，會(huì)清除所有的標(biāo)志位，包括disallowIntercept，所以在使用內(nèi)部攔截法的時(shí)候，我們需要保證外部容器不能攔截DOWN事件，其實(shí)這個(gè)不會(huì)有問(wèn)題的，大不了所有的子View都不處理，最終再扔給你處理。
override fun onInterceptTouchEvent(ev: MotionEvent?): Boolean {
if (ev?.action == MotionEvent.ACTION_DOWN) {
super.onInterceptTouchEvent(ev)
return false
}
return true
}
所以在父容器的onInterceptTouchEvent方法中，不能對(duì)DOWN事件進(jìn)行攔截，這里返回了false。
因?yàn)楦溉萜鳑](méi)有攔截down事件，所以事件被分發(fā)給了子View（可以上下滑動(dòng)），緊接著MOVE事件來(lái)了，全部交給了子View處理，這時(shí)的mFirstTouchTarget還是子View的。如果用戶手勢(shì)改成了左右滑動(dòng)，那么這個(gè)過(guò)程兩者是如何完成轉(zhuǎn)換的呢？
此時(shí)，mFirstTouchTarget != null，action == MOVE，disallowIntercept = false，因?yàn)槭莔ove事件，所有標(biāo)志位不會(huì)被清除，此時(shí)會(huì)走到這里。
if (!disallowIntercept) {
intercepted = onInterceptTouchEvent(ev);
ev.setAction(action); // restore action in case it was changed
}
此時(shí)，父容器的onInterceptTouchEvent返回的是true，要攔截子View的事件了，此時(shí)intercepted = true，因?yàn)閙FirstTouchTarget != null，所以在攔截邏輯里，是會(huì)走到else代碼塊中的。
while (target != null) {
final TouchTarget next = target.next;
if (alreadyDispatchedToNewTouchTarget && target == newTouchTarget) {
handled = true;
} else {
final boolean cancelChild = resetCancelNextUpFlag(target.child)
|| intercepted;
if (dispatchTransformedTouchEvent(ev, cancelChild,
target.child, target.pointerIdBits)) {
handled = true;
}
if (cancelChild) {
if (predecessor == null) {
mFirstTouchTarget = next;
} else {
predecessor.next = next;
}
target.recycle();
target = next;
continue;
}
}
predecessor = target;
target = next;
}
因?yàn)檫@個(gè)時(shí)候 intercepted = true，所以cancelChild = true，所以在dispatchTransformedTouchEvent方法中，第二個(gè)參數(shù)為true。
private boolean dispatchTransformedTouchEvent(MotionEvent event, boolean cancel,
View child, int desiredPointerIdBits) {
final boolean handled;
// Canceling motions is a special case. We don't need to perform any transformations
// or filtering. The important part is the action, not the contents.
final int oldAction = event.getAction();
if (cancel || oldAction == MotionEvent.ACTION_CANCEL) {
event.setAction(MotionEvent.ACTION_CANCEL);
if (child == null) {
handled = super.dispatchTouchEvent(event);
} else {
handled = child.dispatchTouchEvent(event);
}
event.setAction(oldAction);
return handled;
}
}
這時(shí)會(huì)觸發(fā)一個(gè)ACTION_CANCEL事件，這個(gè)事件是子View事件被上層攔截的時(shí)候觸發(fā)的，其實(shí)當(dāng)前這個(gè)MOVE事件做的一件事，就是執(zhí)行了子View的cancel事件，然后將mFirstTouchTarget置為了空；因?yàn)镸OVE事件很多，所以下個(gè)MOVE事件進(jìn)來(lái)之后，又會(huì)走到判斷是否攔截的邏輯中。
此時(shí)父容器會(huì)冷酷地?cái)r截這些MOVE事件，原本屬于子View的MOVE事件，而且不會(huì)往下分發(fā)，走到攔截邏輯中，因?yàn)榇藭r(shí)mFirstTouchTarget為空，所以直接由自身決定是否消費(fèi)，肯定消費(fèi)了，因?yàn)樵谧笥一瑒?dòng)，也就是這樣完成的事件消費(fèi)處理權(quán)的切換。
2.2 外部攔截法
那么對(duì)于外部攔截法，則是需要?jiǎng)討B(tài)修改onInterceptTouchEvent的返回值，如果用戶左右滑動(dòng)，那么就攔截，onInterceptTouchEvent返回true，此時(shí)intercepted = true，就不再走事件分發(fā)流程了。
class MotionEventLayout(
val mContext: Context,
val attrs: AttributeSet? = null,
val defStyleAttr: Int = 0
) : FrameLayout(mContext, attrs, defStyleAttr) {
private var startX = 0f
private var startY = 0f
override fun onInterceptTouchEvent(ev: MotionEvent?): Boolean {
var intercepted = false
when (ev?.action) {
MotionEvent.ACTION_DOWN -> {
}
MotionEvent.ACTION_MOVE -> {
val endX = ev.rawX
val endY = ev.rawY
//豎向滑動(dòng)
intercepted = abs(endX - startX) > abs(endY - startY)
startX = endX
startY = endY
}
}
return intercepted
}
}
相較于內(nèi)部攔截法，外部攔截就顯得比較簡(jiǎn)單了，完全由父容器發(fā)牌決定。
以上就是Android進(jìn)階事件分發(fā)機(jī)制解決事件沖突的詳細(xì)內(nèi)容，更多關(guān)于Android事件沖突解決的資料請(qǐng)關(guān)注腳本之家其它相關(guān)文章！
相關(guān)文章
BottomNavigationView?ViewPager2?Fragment底部菜單導(dǎo)航欄
這篇文章主要為大家介紹了BottomNavigationView?ViewPager2?Fragment底部菜單導(dǎo)航欄實(shí)現(xiàn)效果詳解，有需要的朋友可以借鑒參考下，希望能夠有所幫助，祝大家多多進(jìn)步，早日升職加薪2022-11-11
StreamConfigurationMap和OutputConfiguration是AndroidCamera2API中用于描述和配置相機(jī)輸出流的關(guān)鍵類,本文介紹Android?Camera?API作用及使用指南,感興趣的朋友一起看看吧2025-02-02
淺談關(guān)于Android路由的實(shí)現(xiàn)
本篇文章主要介紹了淺談關(guān)于Android路由的實(shí)現(xiàn)，小編覺(jué)得挺不錯(cuò)的，現(xiàn)在分享給大家，也給大家做個(gè)參考。一起跟隨小編過(guò)來(lái)看看吧2017-10-10
Android實(shí)現(xiàn)下拉放大圖片松手自動(dòng)反彈效果
這篇文章主要為大家詳細(xì)介紹了Android實(shí)現(xiàn)下拉放大圖片松手自動(dòng)反彈效果，具有一定的參考價(jià)值，感興趣的小伙伴們可以參考一下2018-03-03
這篇文章主要介紹了android 使用Xml文件定義Shape方式，具有很好的參考價(jià)值，希望對(duì)大家有所幫助。一起跟隨小編過(guò)來(lái)看看吧2020-03-03
Flutter本身提供了路由機(jī)制，本文主要介紹了Flutter fluro配置使用，文中通過(guò)示例代碼介紹的非常詳細(xì)，具有一定的參考價(jià)值，感興趣的小伙伴們可以參考一下2021-09-09
Android TextView 設(shè)置字體大小的方法
這篇文章主要介紹了Android TextView 設(shè)置字體大小的方法的相關(guān)資料,需要的朋友可以參考下2016-02-02
Android Init進(jìn)程對(duì)信號(hào)的處理流程詳細(xì)介紹
這篇文章主要介紹了Android Init進(jìn)程對(duì)信號(hào)的處理流程詳細(xì)介紹的相關(guān)資料,需要的朋友可以參考下2017-02-02
我們?cè)陂_發(fā)中肯定會(huì)經(jīng)常用Kotlin提供的一些通用拓展函數(shù),當(dāng)我們進(jìn)去看源碼的時(shí)候會(huì)發(fā)現(xiàn)許多函數(shù)里面有contract{}包裹的代碼塊,那么這些代碼塊到底有什么作用呢?下面這篇文章主要給大家介紹了關(guān)于Kotlin中contract到底有什么用的相關(guān)資料,需要的朋友可以參考下2022-01-01
flutter實(shí)現(xiàn)帶刪除動(dòng)畫的listview功能
最近接了一個(gè)新項(xiàng)目，需要開發(fā)帶有刪除動(dòng)畫效果的listview功能，在實(shí)現(xiàn)過(guò)程中列表滾動(dòng)效果用listview實(shí)現(xiàn)的，本文通過(guò)實(shí)例代碼給大家分享實(shí)現(xiàn)過(guò)程，感興趣的朋友跟隨小編一起學(xué)習(xí)下吧2021-05-05